Recently, an optical unit including a rotary reflector that rotates in one direction around its rotation axis while reflecting light emitted from a light source has been devised (see JPWO 2011129105 (A1)).
This optical unit can form a light distribution pattern partially shielded by controlling the timing of the turning on/off of the light source while scanning the front side of the optical unit with a light source image.
By the way, when the change in brightness in the vicinity of a bright/dark boundary of a light-shielding portion formed in a part of a light distribution pattern is sharp, a sense of discomfort may be given to a viewer of the light distribution pattern. On the other hand, when the change in brightness in the vicinity of the bright/dark boundary is too gentle, the range of the light-shielding portion becomes unclear, and hence, there is a concern that visibility of an end portion of an irradiation region adjacent to the light-shielding portion is deteriorated.